Sheet lateral positioning device

ABSTRACT

An apparatus for registering a sheet along a transport path, including a plurality of spaced apart sheet feeding nip sets of plural sheet feeding nips in the sheet transport path, the plural sheet feeding nips of the sheet feeding nip sets comprise plural drive wheels and plural mating idlers, steerable drive mechanism for changing the drive wheel to idler alignment to thereby transport the sheet along the paper path while imparting a lateral motion to the sheet as it is transported along the paper path.

BACKGROUND AND SUMMARY

This invention relates generally to a sheet transport system, and more particularly concerns an apparatus and method for adjusting sheet position along an axis substantially orthogonal to the transport direction, referred to herein as the lateral axis, in a high speed printing machine.

In a typical electrophotographic printing process, a photoconductive member is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive member is exposed to a light image of an original document being reproduced. Exposure of the charged photoconductive member selectively dissipates the charges thereon in the irradiated areas. This records an electrostatic latent image on the photoconductive member corresponding to the informational areas contained within the original document. After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing a developer material into contact therewith. Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules to the latent image forming a toner powder image on the photoconductive member. The toner powder image is then transferred from the photoconductive member to a copy sheet. The toner particles are heated to permanently affix the powder image to the copy sheet.

High quality documents require registration of sheets of paper or other substrate to the photoreceptor for image transfer. Accurate registration control locates the image consistently with respect to the edge of the paper. Typical registration devices require that incoming sheets arrive within a specific lateral range in order to be properly registered. Additionally, other devices, such as compiling trays within an output module, require that incoming sheets arrive within a specific lateral range in order to be properly processed. However, as printing systems become larger and more complex, it becomes increasingly difficult to maintain control of the lateral position of sheets within the system. This invention describes a device for adjusting the lateral position of a sheet in a paper path using relatively inexpensive components.

In accordance with one aspect of the present invention there is provided an apparatus for registering a sheet along a transport path, including a plurality of spaced apart sheet feeding nip sets of plural sheet feeding nips in said sheet transport path, said plural sheet feeding nips of said sheet feeding nip sets comprise plural drive wheels and plural mating idlers, steerable mechanism for changing the idler alignment relative to its respective drive wheel to thereby transport said sheet along the paper path while imparting a lateral motion to the sheet as it is transported along the paper path.

Other features of the present invention will become apparent as the following description proceeds and upon reference to the drawings, in which:

FIG. 1 is a schematic elevational view depicting an illustrative electrophotographic printing machine incorporating a sheet registration device of the present invention;

FIG. 2 is a detailed plan view of the sheet registration device;

FIG. 3 is a plan view of the sheet registration device illustrating the method of operation thereof

While the present invention will be described in connection with a preferred embodiment thereof, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.

For a general understanding of the features of the present invention, reference is made to the drawings. In the drawings, like reference numerals have been used throughout to identify identical elements. FIG. 1 schematically depicts an electrophotographic printing machine incorporating the features of the present invention therein. It will become evident from the following discussion that the set transfer device of the present invention may be employed in a wide variety of machines and is not specifically limited in its application to the particular embodiment depicted herein.

Referring to FIG. 1 of the drawings, the electrophotographic printing machine employs a photoconductive belt 10. Preferably, the photoconductive belt 10 is made from a photoconductive material coated on a ground layer, which, in turn, is coated on an anti-curl backing layer. The photoconductive material is made from a transport layer coated on a selenium generator layer. The transport layer transports positive charges from the generator layer. The generator layer is coated on an interface layer. The interface layer is coated on the ground layer made from a titanium coated MYLAR®. The interface layer aids in the transfer of electrons to the ground layer. The ground layer is very thin and allows light to pass therethrough. Other suitable photoconductive materials, ground layers, and anti-curl backing layers may also be employed. Belt 10 moves in the direction of arrow 12 to advance successive portions sequentially through the various processing stations disposed about the path of movement thereof. Belt 10 is entrained about stripping roller 14, tensioning roller 16, idler roll 18 and drive roller 20. Stripping roller 14 and idler roller 18 are mounted rotatably so as to rotate with belt 10. Tensioning roller 16 is resiliently urged against belt 10 to maintain belt 10 under the desired tension. Drive roller 20 is rotated by a motor coupled thereto by suitable means such as a belt drive. As roller 20 rotates, it advances belt 10 in the direction of arrow 12.

Initially, a portion of the photoconductive surface passes through charging station A. At charging station A, two corona generating devices indicated generally by the reference numerals 22 and 24, charge the photoconductive belt 10 to a relatively high, substantially uniform potential. Corona generating device 22 places all of the required charge on photoconductive belt 10. Corona generating device 24 acts as a leveling device, and fills in any areas missed by corona generating device 22. Next, the charged portion of the photoconductive surface is advanced through imaging station B.

At imaging station B, a raster output scanner (ROS), indicated generally by the reference numeral 26, discharges selectively those portions of the charge corresponding to the image portions of the document to be reproduced. In this way, an electrostatic latent image is recorded on the photoconductive surface. An electronic subsystem (ESS), indicated generally by the reference numerals 28, controls ROS 26. ESS 28 is adapted to receive signals from a computer and transpose these signals into suitable signals for controlling ROS 26 so as to record an electrostatic latent image corresponding to the document to be reproduced by the printing machine. ROS 26 may include a laser with a rotating polygon mirror block. The ROS 26 illuminates the charged portion of the photoconductive surface. In this way, a raster electrostatic latent image is recorded on the photoconductive surface which corresponds to the desired information to be printed on the sheet. Other types of imaging systems may also be used employing, for example, a pivoting or shiftable LED write bar or projection LCD (liquid crystal display) or other electro-optic display as the “write” source.

Thereafter, belt 10 advances the electrostatic latent image recorded thereon to development station C. Development station C has three magnetic brush developer rolls indicated generally by the reference numerals 34, 36 and 38. A paddle wheel picks up developer material and delivers it to the developer rolls. When the developer material reaches rolls 34 and 36, it is magnetically split between the rolls with half of the developer material being delivered to each roll. Photoconductive belt 10 is partially wrapped about rolls 34 and 36 to form extended development zones. Developer roll 38 is a clean-up roll. A magnetic roll, positioned after developer roll 38, in the direction of arrow 12 is a carrier granule removal device adapted to remove any carrier granules adhering to belt 10. Thus, rolls 34 and 36 advance developer material into contact with the electrostatic latent image. The latent image attracts toner particles from the carrier granules of the developer material to form a toner powder image on the photoconductive surface of belt 10. Belt 10 then advances the toner powder image to transfer station D.

At transfer station D, a copy sheet is moved into contact with the toner powder image. First, photoconductive belt 10 is exposed to a pre-transfer light from a lamp (not shown) to reduce the attraction between photoconductive belt 10 and the toner powder image. Next, a corona generating device 40 charges the copy sheet to the proper magnitude and polarity so that the copy sheet is tacked to photoconductive belt 10 and the toner powder image attracted from the photoconductive belt to the copy sheet. After transfer, corona generator 42 charges the copy sheet to the opposite polarity to detack the copy sheet from belt 10. Conveyor 44 advances the copy sheet to fusing station E.

Fusing station E includes a fuser assembly indicated generally by the reference numeral 46 which permanently affixes the transferred toner powder image to the copy sheet. Preferably, fuser assembly 46 includes a heated fuser roller 48 and a pressure roller 50 with the powder image on the copy sheet contacting fuser roller 48. The pressure roller is cammed against the fuser roller to provide the necessary pressure to fix the toner powder image to the copy sheet. The fuser roll is internally heated by a quartz lamp. Release agent, stored in a reservoir, is pumped to a metering roll. A trim blade trims off the excess release agent. The release agent transfers to a donor roll and then to the fuser roll.

After fusing, the copy sheets are fed through a decurler 52. Decurler 52 bends the copy sheet in one direction to put a known curl in the copy sheet and then bends it in the opposite direction to remove that curl. Forwarding rollers 54 then advance the sheet to duplex turn roll 56. Duplex solenoid gate 58 guides the sheet to the finishing station F, or to duplex tray 60. At finishing station F, copy sheets are stacked in a compiler tray and attached to one another to form sets. The sheets can be attached to one another by either a binder or a stapler. In either case, a plurality of sets of documents is formed in finishing station F. When duplex solenoid gate 58 diverts the sheet into duplex tray 60. Duplex tray 60 provides an intermediate or buffer storage for those sheets that have been printed on one side and on which an image will be subsequently printed on the second, opposite side thereof, i.e., the sheets being duplexed. The sheets are stacked in duplex tray 60 face down on top of one another in the order in which they are copied.

In order to complete duplex copying, the simplex sheets in tray 60 are fed, in seriatim, by bottom feeder 62 from tray 60 back to transfer station D via conveyor 64 and rollers 66 for transfer of the toner powder image to the opposed sides of the copy sheets. Inasmuch as successive bottom sheets are fed from duplex tray 60, the proper or clean side of the copy sheet is positioned in contact with belt 10 at transfer station D so that the toner powder image is transferred thereto. The duplex sheet is then fed through the same path as the simplex sheet to be advanced to finishing station F.

Copy sheets are fed to transfer station D from the secondary tray 68. The secondary tray 68 includes an elevator driven by a bidirectional AC motor. Its controller has the ability to drive the tray up or down. When the tray is in the down position, stacks of copy sheets are loaded thereon or unloaded therefrom. In the up position, successive copy sheets may be fed therefrom by sheet feeder 70. Sheet feeder 70 is a friction retard feeder utilizing a feed belt and take-away rolls to advance successive copy sheets to transport 64 which advances the sheets to rolls 98 which feed the sheets to the registration device of the invention herein, described in detail below, and then to transfer station D.

Copy sheets may also be fed to transfer station D from the auxiliary tray 72. The auxiliary tray 72 includes an elevator driven by a directional AC motor. Its controller has the ability to drive the tray up or down. When the tray is in the down position, stacks of copy sheets are loaded thereon or unloaded therefrom. In the up position, successive copy sheets may be fed therefrom by sheet feeder 74. Sheet feeder 74 is a friction retard feeder utilizing a feed belt and take-away rolls to advance successive copy sheets to transport 64 which advances the sheets to rolls 98 to the registration device and then to transfer station D.

Secondary tray 68 and auxiliary tray 72 are secondary sources of copy sheets. The high capacity sheet feeder, indicated generally by the reference numeral 76, is the primary source of copy sheets. Feed belt 81 feeds successive uppermost sheets from the stack to a take-away drive roll 82 and idler rolls 84. The drive roll and idler rolls guide the sheet onto transport 86. Transport 86 advances the sheet to rolls 98 which, in turn, move the sheet through the registration device to transfer station D.

Invariably, after the copy sheet is separated from the photoconductive belt 10, some residual particles remain adhering thereto. After transfer, photoconductive belt 10 passes beneath corona generating device 94 which charges the residual toner particles to the proper polarity. Thereafter, the pre-charge erase lamp (not shown), located inside photoconductive belt 10, discharges the photoconductive belt in preparation for the next charging cycle. Residual particles are removed from the photoconductive surface at cleaning station G. Cleaning station G includes an electrically biased cleaner brush 88 and two de-toning rolls. The reclaim roll is electrically biased negatively relative to the cleaner roll so as to remove toner particles therefrom. The waste roll is electrically biased positively relative to the reclaim roll so as to remove paper debris and wrong sign toner particles. The toner particles on the reclaim roll are scraped off and deposited in a reclaim auger (not shown), where it is transported out of the rear of cleaning station G.

The various machine functions are regulated by a controller 29. The controller 29 is preferably a programmable microprocessor which controls the entire machine functions hereinbefore described. The controller provides a comparison count of the copy sheets, the number of documents being recirculated, the number of copy sheets selected by the operator, time delays, jam corrections, etc. The control of all of the exemplary systems heretofore described may be accomplished by conventional control switch inputs from the printing machine consoles selected by the operator. Conventional sheet path sensors or switches may be utilized to keep track of the position of the document and the copy sheets. In addition, the controller regulates the various positions of the gates depending upon the mode of operation selected.

The invention herein has been illustrated in a high speed black and white printing machine. It is also very suitable for use in a high speed full color or highlight color printing machine where accurate sheet registration is critical.

High quality documents require registration of sheets of paper to the photoreceptor for image transfer. Accurate registration control locates the image consistently with respect to the edge of the paper. In order to provide this accurate registration control, the registration device accepts incoming sheets having unknown position and orientation and delivers them to transfer station D with the sheet edges aligned to predetermined datums. The registration device performs this function over a limited range of incoming sheet position and orientation. Notably, there is a limited range of lateral position that the registration device can accommodate. In many systems, this condition may be difficult to guarantee because of the various and potentially long paths that sheets may take from various sources such as feeders or duplex paths. Because of manufacturing tolerances and wear effects, it is typical that the average lateral incoming sheet position from each of these various sources can vary substantially from one another. It is therefore desired to have a compact and inexpensive means to adjust the average lateral incoming position of sheets from one or more of these sources in order to reduce the total incoming lateral sheet variation that is delivered to the registration device.

FIG. 2 shows a device suitable for adjusting the lateral position of the paper. Axles 302-308 are driven by a common direct drive motor, timing belt drive system or any other suitable drive method (not shown). The accuracy of this drive is not very important and thus can be inexpensive. Mounted on axles 302-308 are drive rollers. Axles 202-208 have mounted thereon idle rollers which are mounted above respective drive rollers thus forming a sheet feeding nip set. Axles 302-308 are mounted in a fixed position and are aligned in a position substantially parallel to each other and parallel to the lateral axis of the paper path. Axles 203-207 are connected to each other by a steering mechanism 200 in which axles 203-207 are aligned and pivot in a position substantially parallel to each other. Steering mechanism 200 is connected to an actuator which positions the angle of the axles 203-207 thereby changing each idler roller alignment relative to its respective drive roller. Steering control can be accomplished by a mechanical actuator such as an adjustment screw or rotary cam, not shown. It is also possible for the actuator to be a solenoid or stepper/dc motor with lead screw with stops or home sensors.

It has been observed that sheets will walk in the lateral axis along a paper transport depending on the idler roll alignment to the drive rolls. So long as the first nip and last nip in a transport are parallel, the net skew induced in the sheet is substantially zero, but the net lateral walk can be significant. This behavior has been found to occur when using elastomeric drive rolls together with thermoplastic idler rolls. The lateral compliance, or the amount that a roll elastically distorts along its lateral axis when subjected to a tangential force parallel to the lateral axis, is a function of the roll material properties. It has been observed that the lateral compliance of an elastomeric drive roll is substantially higher than that of a thermoplastic idler roll. It has further been observed that, under the above circumstances, the sheet motion will tend to align to the idler rolls. So deliberately misaligning the idler shafts relative to the drive shafts in a sheet transport in order to induce lateral walk in the sheet. This effect can be used to correct for average shifts in lateral sheet position that may have accumulated in prior transports. It is possible to simply adjust one or several of the intermediate idler shafts to a plus, neutral, or minus setting to achieve varying degrees of lateral walk in the transport. The present disclosure makes alignment much easier than moving the whole modules.

FIG. 3 illustrates the sheet motion achieved by using the described strategy. Actuator 102 has adjusted the idler axles 203, 204, 205, 206 and 207 to a counterclockwise rotation relative to the drive roll axles, not shown. As a sheet enters nip formed by idler axle 203, a small skew angle is formed. As the sheet advances further, this skew angle is maintained and the sheet moves laterally according to the idler axle alignment. As the sheet reaches the nip formed by idler axle 208, an opposite skew is formed, thus resulting in substantially zero net skew imparted to the sheet. However, it can be seen that a net lateral shift in the sheet position has been achieved. The actuator adjustment is made based upon the average exiting lateral position of sheets, so that the next downstream transport, such as a registration device, receives sheets within a predefined lateral position range. The actuator adjustments can be made manually by an operator or can be made automatically by a suitable controller. If, for example, a sensor 134 is provided near the exit of the transport, and if sensor 134 is placed at the desired lateral exit position of the transport, then the actuator can automatically vary the idler axle alignment until the average sheet exit lateral position corresponds to sensor 134 location.

In recapitulation, there is provided an apparatus for laterally positioning a sheet along a transport path, including a plurality of spaced apart sheet feeding nip sets of plural sheet feeding nips in said sheet transport path, said plural sheet feeding nips of said sheet feeding nip sets comprise plural drive wheels and plural mating idlers, steerable drive mechanism for changing the idler alignment relative to the respective drive wheel to thereby transport said sheet along the paper path while imparting a lateral motion to the sheet as it is transported along the paper path.

It is, therefore, apparent that there has been provided in accordance with the present invention, a sheet registration device that fully satisfies the aims and advantages hereinbefore set forth. While this invention has been described in conjunction with a specific embodiment thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.

It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims. Unless specifically recited in a claim, steps or components of claims should not be implied or imported from the specification or any other claims as to any particular order, number, position, size, shape, angle, color, or material. 

1. An apparatus for laterally positioning a sheet along a transport path, comprising: a plurality of spaced apart sheet feeding nip sets in said sheet transport path, each one of the sheet feeding nip sets comprise drive wheels and mating idlers, a steerable drive mechanism for changing the mating idlers drive wheels alignment to thereby transport the sheet along the paper path while imparting a lateral motion to the sheet as the sheet is transported along the paper path; and an entrance sheet feeding nip and an exit sheet feeding nip, said entrance sheet feeding nip and said exit sheet feeding nip having both drive wheels and mating idlers aligned parallel relative to each other.
 2. An apparatus according to claim 1, wherein said drive wheels are mounted on one of the drive shafts in a fixed position and are aligned in a position substantially perpendicular to said paper path transport direction.
 3. An apparatus according to claim 2, wherein each of said mating idlers are mounted on one of the idler shafts wherein each one of said idler shafts being rotatable about an axis perpendicular to the transport plane.
 4. An apparatus according to claim 3, further comprising an actuator for rotating said idler drive shafts so that the sheet is moved both in a direction along the paper path and a lateral direction to the path.
 5. An apparatus according to claim 4, further comprising a sensor located along an edge of the sheet in the paper path.
 6. An apparatus according to claim 5, further comprising a controller, responsive to a signal from said sensor, for rotating said idler shafts so that the sheet is moved both in a direction along the paper path and a lateral direction to the path.
 7. An apparatus according to claim 4, wherein said actuator comprises a rack and pinion system having connecting members connects each one of said idler shafts for common movement.
 8. (canceled)
 9. An apparatus according to claim 3, wherein lateral compliance of said mating idlers is less than or equal to one half the lateral compliance of said drive wheels.
 10. A method of laterally positioning a sheet, consisting of: feeding said sheet into a first pinch nip having a first orientation; successively feeding said sheet into successive pinch nips having a second orientation in which the idlers of each successive nip are aligned to one another and are aligned differently than the idlers of the first pinch nip; feeding said sheet to a final pinch nip having said first orientation. 